1. Field of the Invention
This invention relates to plate/fin-type heat exchangers, and more specifically, to a unibody open-faced plate for plate/fin-type heat exchangers using countercurrent or parallel flow.
2. Description of the Prior Art
The plate/fin-type heat exchangers are mainly of the channel and rib type construction. Countercurrent flow can be achieved; however, manifolding a plate stack which must separate the fluids at entry and exit becomes extremely complex. In that manifolding of the crosscurrent heat exchangers is comparatively simple, this heat exchanger system is more widely used although it is less efficient than the countercurrent system and it induces serious thermal and mechanical stresses.
One countercurrent system which has attempted to solve the manifolding problem of the countercurrent heat exchanger is taught by Campbell et al, U.S. Pat. No. 3,305,010. Campbell et al teach a heat exchanger having superposed stacked plate and fin elements and complex manifolding means for introducing fluids of different temperatures into opposite ends of the assembly. However, Campbell et al do not teach a plate which serves as both the plate and the fin, nor does Campbell et al teach means for internally manifolding the plate within the plate's plane.
Another countercurrent system, FIG. 1, is that of Alfa-Laval described in The Proceedings of the 5th OTEC Conference, Miami, Florida (Feb. 1978) Pages VI 288-320. The Alfa-Laval concept consists mainly of a pack of thin metal plates, a frame and means of keeping the pieces together. The plates are suspended between horizontal carrying bars at top and bottom and compressed against the stationary frame plate by means of tightening bolts and a movable pressure plate. The frame plate is equipped with nozzles for inlet and outlet connections. Every plate is sealed around its perimeter with a gasket and cemented into a pressed track. Flow ports at each of the plate corners are individually gasketed and thus divide the interplate spaces into two systems of alternating flow channels. Through these, the two media pass, the warmer medium giving up heat to the cooler by conduction through the thin plates. This gasket arrangement eliminates the risk of media interleakage. The plate, which is the basic element of this concept, has a corrugated pattern stamped on it. These corrugations can be arranged to create an unlimited number of plate patterns. The specific pattern results from a careful trade-off between pressure drop and convective heat transfer characteristics.
The gaskets in the Alfa-Laval system are cemented to the plates in pressed tracks, and are generally made of elastomers like natural rubber, nitrile, butyl, neoprene, viton, etc. The material selection depends upon the working conditions; however, the upper limits are about 360 PSI and about 400.degree. F.
The present invention can be distinguished from that of Alfa-Laval in many ways, some of which include: (1) that the Alfa-Laval system requires gaskets which limit operating pressure and temperature; (2) that the Alfa-Laval system has no contact fins or essential flat plate bottoms for providing the plate-to-plate contact necessary to obtain the optimum heat transfer coefficient; (3) the fact that the inlets and outlets of the Alfa-Lavel system are positioned on opposite ends but on the same side of the plate results in a maldistribution of flow across the plate and inefficient heat transfer; and (4) that Alfa-Laval provides no means for driving the incoming fluid across the face of the plate, thereby correcting for their inherent inefficiencies.
Finally, it should be noted that the aforementioned prior art does not teach an annular plate structure nor the plate segment of the present invention.